Re: [PATCH] libstdc++: Declare const global variables inline

[Jonathan Wakely <jwakely@redhat.com>]

On Wed, 2 Nov 2022 at 13:42, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> IIUC such variables should be declared inline to avoid potential ODR
> violations since they're otherwise considered to be distinct (internal
> linkage) entities across TUs.
>
> The changes inside the regex_constants and execution namespace seem to
> be unimplemented parts of P0607R0; the rest of the changes touch only
> implementation details.
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

OK, thanks.

My understanding was that [basic.def.odr] p14.5 means we don't get ODR
violations, but I think that only works for sensible uses of the
variables. Any inline function that takes the address of (or binds a
reference to) one of these variables will get an ODR violation. So the
patch is an improvement.


>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/atomic_wait.h (_detail::__platform_wait_alignment):
>         Declare inline.  Remove redundant static specifier.
>         (__detail::__atomic_spin_count_relax): Declare inline.
>         (__detail::__atomic_spin_count): Likewise.
>         * include/bits/regex_automaton.h (__detail::_S_invalid_state_id):
>         Conditionally declare inline.  Declare constexpr.  Remove
>         redundant const and static specifiers.
>         * include/bits/regex_error.h (regex_constants::error_collate): Conditionally
>         declare inline.
>         (regex_constants::error_ctype): Likewise.
>         (regex_constants::error_escape): Likewise.
>         (regex_constants::error_backref): Likewise.
>         (regex_constants::error_brack): Likewise.
>         (regex_constants::error_paren): Likewise.
>         (regex_constants::error_brace): Likewise.
>         (regex_constants::error_badbrace): Likewise.
>         (regex_constants::error_range): Likewise.
>         (regex_constants::error_space): Likewise.
>         (regex_constants::error_badrepeat): Likewise.
>         (regex_constants::error_complexity): Likewise.
>         (regex_constants::error_stack): Likewise.
>         * include/ext/concurrence.h (__gnu_cxx::__default_lock_policy):
>         Likewise.  Remove redundant static specifier.
>         * include/pstl/execution_defs.h (execution::seq): Conditionally declare
>         inline.
>         (execution::par): Likewise.
>         (execution::par_unseq): Likewise.
>         (execution::unseq): Likewise.
> ---
>  libstdc++-v3/include/bits/atomic_wait.h     |  8 +++----
>  libstdc++-v3/include/bits/regex_automaton.h |  2 +-
>  libstdc++-v3/include/bits/regex_error.h     | 26 ++++++++++-----------
>  libstdc++-v3/include/ext/concurrence.h      |  2 +-
>  libstdc++-v3/include/pstl/execution_defs.h  |  8 +++----
>  5 files changed, 23 insertions(+), 23 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h
> index 76ed7409937..bd1ed56d157 100644
> --- a/libstdc++-v3/include/bits/atomic_wait.h
> +++ b/libstdc++-v3/include/bits/atomic_wait.h
> @@ -58,14 +58,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>  #ifdef _GLIBCXX_HAVE_LINUX_FUTEX
>  #define _GLIBCXX_HAVE_PLATFORM_WAIT 1
>      using __platform_wait_t = int;
> -    static constexpr size_t __platform_wait_alignment = 4;
> +    inline constexpr size_t __platform_wait_alignment = 4;
>  #else
>  // define _GLIBCX_HAVE_PLATFORM_WAIT and implement __platform_wait()
>  // and __platform_notify() if there is a more efficient primitive supported
>  // by the platform (e.g. __ulock_wait()/__ulock_wake()) which is better than
>  // a mutex/condvar based wait.
>      using __platform_wait_t = uint64_t;
> -    static constexpr size_t __platform_wait_alignment
> +    inline constexpr size_t __platform_wait_alignment
>        = __alignof__(__platform_wait_t);
>  #endif
>    } // namespace __detail
> @@ -142,8 +142,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>  #endif
>      }
>
> -    constexpr auto __atomic_spin_count_relax = 12;
> -    constexpr auto __atomic_spin_count = 16;
> +    inline constexpr auto __atomic_spin_count_relax = 12;
> +    inline constexpr auto __atomic_spin_count = 16;
>
>      struct __default_spin_policy
>      {
> diff --git a/libstdc++-v3/include/bits/regex_automaton.h b/libstdc++-v3/include/bits/regex_automaton.h
> index f95eb7dad6d..44bde42e212 100644
> --- a/libstdc++-v3/include/bits/regex_automaton.h
> +++ b/libstdc++-v3/include/bits/regex_automaton.h
> @@ -46,7 +46,7 @@ namespace __detail
>     */
>
>    typedef long _StateIdT;
> -  static const _StateIdT _S_invalid_state_id  = -1;
> +  _GLIBCXX17_INLINE constexpr _StateIdT _S_invalid_state_id  = -1;
>
>    template<typename _CharT>
>      using _Matcher = std::function<bool (_CharT)>;
> diff --git a/libstdc++-v3/include/bits/regex_error.h b/libstdc++-v3/include/bits/regex_error.h
> index 74a1428c2c7..ab207650d44 100644
> --- a/libstdc++-v3/include/bits/regex_error.h
> +++ b/libstdc++-v3/include/bits/regex_error.h
> @@ -66,60 +66,60 @@ namespace regex_constants
>      };
>
>    /** The expression contained an invalid collating element name. */
> -  constexpr error_type error_collate(_S_error_collate);
> +  _GLIBCXX17_INLINE constexpr error_type error_collate(_S_error_collate);
>
>    /** The expression contained an invalid character class name. */
> -  constexpr error_type error_ctype(_S_error_ctype);
> +  _GLIBCXX17_INLINE constexpr error_type error_ctype(_S_error_ctype);
>
>    /**
>     * The expression contained an invalid escaped character, or a trailing
>     * escape.
>     */
> -  constexpr error_type error_escape(_S_error_escape);
> +  _GLIBCXX17_INLINE constexpr error_type error_escape(_S_error_escape);
>
>    /** The expression contained an invalid back reference. */
> -  constexpr error_type error_backref(_S_error_backref);
> +  _GLIBCXX17_INLINE constexpr error_type error_backref(_S_error_backref);
>
>    /** The expression contained mismatched [ and ]. */
> -  constexpr error_type error_brack(_S_error_brack);
> +  _GLIBCXX17_INLINE constexpr error_type error_brack(_S_error_brack);
>
>    /** The expression contained mismatched ( and ). */
> -  constexpr error_type error_paren(_S_error_paren);
> +  _GLIBCXX17_INLINE constexpr error_type error_paren(_S_error_paren);
>
>    /** The expression contained mismatched { and } */
> -  constexpr error_type error_brace(_S_error_brace);
> +  _GLIBCXX17_INLINE constexpr error_type error_brace(_S_error_brace);
>
>    /** The expression contained an invalid range in a {} expression. */
> -  constexpr error_type error_badbrace(_S_error_badbrace);
> +  _GLIBCXX17_INLINE constexpr error_type error_badbrace(_S_error_badbrace);
>
>    /**
>     * The expression contained an invalid character range,
>     * such as [b-a] in most encodings.
>     */
> -  constexpr error_type error_range(_S_error_range);
> +  _GLIBCXX17_INLINE constexpr error_type error_range(_S_error_range);
>
>    /**
>     * There was insufficient memory to convert the expression into a
>     * finite state machine.
>     */
> -  constexpr error_type error_space(_S_error_space);
> +  _GLIBCXX17_INLINE constexpr error_type error_space(_S_error_space);
>
>    /**
>     * One of <em>*?+{</em> was not preceded by a valid regular expression.
>     */
> -  constexpr error_type error_badrepeat(_S_error_badrepeat);
> +  _GLIBCXX17_INLINE constexpr error_type error_badrepeat(_S_error_badrepeat);
>
>    /**
>     * The complexity of an attempted match against a regular expression
>     * exceeded a pre-set level.
>     */
> -  constexpr error_type error_complexity(_S_error_complexity);
> +  _GLIBCXX17_INLINE constexpr error_type error_complexity(_S_error_complexity);
>
>    /**
>     * There was insufficient memory to determine whether the
>     * regular expression could match the specified character sequence.
>     */
> -  constexpr error_type error_stack(_S_error_stack);
> +  _GLIBCXX17_INLINE constexpr error_type error_stack(_S_error_stack);
>
>    ///@}
>  } // namespace regex_constants
> diff --git a/libstdc++-v3/include/ext/concurrence.h b/libstdc++-v3/include/ext/concurrence.h
> index aea861b534f..7fd81490eff 100644
> --- a/libstdc++-v3/include/ext/concurrence.h
> +++ b/libstdc++-v3/include/ext/concurrence.h
> @@ -50,7 +50,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
>    // Compile time constant that indicates prefered locking policy in
>    // the current configuration.
> -  static const _Lock_policy __default_lock_policy =
> +  _GLIBCXX17_INLINE const _Lock_policy __default_lock_policy =
>  #ifndef __GTHREADS
>    _S_single;
>  #elif defined _GLIBCXX_HAVE_ATOMIC_LOCK_POLICY
> diff --git a/libstdc++-v3/include/pstl/execution_defs.h b/libstdc++-v3/include/pstl/execution_defs.h
> index 13b002931e8..3eca558dac2 100644
> --- a/libstdc++-v3/include/pstl/execution_defs.h
> +++ b/libstdc++-v3/include/pstl/execution_defs.h
> @@ -107,10 +107,10 @@ class unsequenced_policy
>  };
>
>  // 2.8, Execution policy objects
> -constexpr sequenced_policy seq{};
> -constexpr parallel_policy par{};
> -constexpr parallel_unsequenced_policy par_unseq{};
> -constexpr unsequenced_policy unseq{};
> +_GLIBCXX17_INLINE constexpr sequenced_policy seq{};
> +_GLIBCXX17_INLINE constexpr parallel_policy par{};
> +_GLIBCXX17_INLINE constexpr parallel_unsequenced_policy par_unseq{};
> +_GLIBCXX17_INLINE constexpr unsequenced_policy unseq{};
>
>  // 2.3, Execution policy type trait
>  template <class _Tp>
> --
> 2.38.1.381.gc03801e19c
>